Rebar harmonic. .. ?

[Johnhamdun]

Yes, an infinate number of octaves in theory.  I never thought of every note being there too in a vibrating string.

You want to heard something along those lines that's even cooler? If you play a note through different pieces of wood the end signal comes out with its harmonics heightened and lowered at different points. In other words, with one type of wood (cedar lets say) the fifth and seventh harmonics might be accentuated while with another type of wood (spruce or something) the ninth and 14th harmonic could be accentuated. So, taking it one step further different pieces of wood play different chords every time you play a note.

I know that all of that is true and Ive used that as my theoretical explanation for why different woods are considered tone woods. Kind of makes sense right? If I play an A note I would rather have a major chord played back to me than some random collection of notes.

 

[jmasin]

Yes, an infinate number of octaves in theory.  I never thought of every note being there too in a vibrating string.

You want to heard something along those lines that's even cooler? If you play a note through different pieces of wood the end signal comes out with its harmonics heightened and lowered at different points. In other words, with one type of wood (cedar lets say) the fifth and seventh harmonics might be accentuated while with another type of wood (spruce or something) the ninth and 14th harmonic could be accentuated. So, taking it one step further different pieces of wood play different chords every time you play a note.

I know that all of that is true and Ive used that as my theoretical explanation for why different woods are considered tone woods. Kind of makes sense right? If I play an A note I would rather have a major chord played back to me than some random collection of notes.

Please note that a harmonic is an integer multiple of the fundamental frequency.  So 440Hz, 880Hz, 1320Hz etc.  So the fact that different harmonics are present does not mean different chords, it means a different mix of the octaves.

The accentuation of different harmonics by an instrument is called "timbre" and is why some instruments sound different than others.

An "A, 440Hz" played by a piano is easily recognized from an "A, 440Hz" played by a guitar (as are the multiple A/440Hz's on different strings).

 

[NeilStryker]

Overtones are more accurately what we're talking about.  Overtones can be harmonics, but not always.

 

[TimC]

Please note that a harmonic is an integer multiple of the fundamental frequency.  So 440Hz, 880Hz, 1320Hz etc.  So the fact that different harmonics are present does not mean different chords, it means a different mix of the octaves.
The accentuation of different harmonics by an instrument is called "timbre" and is why some instruments sound different than others.
An "A, 440Hz" played by a piano is easily recognized from an "A, 440Hz" played by a guitar (as are the multiple A/440Hz's on different strings).

There are 3rds and 5ths strong enough to heard in the note played. If there are 3rds and 5ths. then their 3ds and 5ths are also present and it goes on and on. These are not there with enough amplitude to really effect the tone of the note though.

 

[jmasin]

Overtones are more accurately what we're talking about.  Overtones can be harmonics, but not always.

Agreed.

[quote author=TimC]
There are 3rds and 5ths strong enough to heard in the note played. If there are 3rds and 5ths. then their 3ds and 5ths are also present and it goes on and on. These are not there with enough amplitude to really effect the tone of the note though.
[/quote]

That's cool I thought you just meant harmonics.  No offense intended.

I'll be the first to admit I do not know how many inharmonics are generated when striking a single string on the guitar.  It would be interesting to hook up a frequency analyzer and see.  Maybe I'll borrow one from work one day (not being a smart alec, it really would be interesting).

Cheers.   ccasion14:

 

[TimC]

No offense taken jmasin. I was more or less thinking out loud about Johnhamdun's post. I'm hardly an acoustic engineer. In fact, I've reached the age where I don't know what I know anymore.  :icon_biggrin:

 

[jmasin]

Hey Tim,

Being the complete nerd that I am, I actually made some measurements.  I'm new to theory and such, so some of this is clearly known to all, but I owe you a bit of an apology.  I was thinking only harmonics that are a multiple of two (octaves) and didn't realize until it was right in front of me that 3rd and 5ths are actually different notes (again, new to theory so apologies).  Anyway, below is pretty cool (keeping in mind I'm an engineer ).

Here's an open A (110Hz) played through my bassman (clean) through different pickups.  I was surprised to see that some harmonics are actually equal or greater in amplitude than the fundamental for an open string.  The colors didn't turn out so well in conversion to jpg, but the middle clearly favors the 3rd and 4th and the neck pickup favors the 5th and 6th harmonics for the open A.

Here's the 440Hz A played on the G-string.  Interesting that the higher order harmonics are much reduced; however, here it is clear that the bridge pickup get's these. 

Like I said, maybe I just reinvented the wheel for most of you, but I thought it was neat, I learned something and had fun, so there!

ccasion14:

 

[TimC]

Good piece of work jmasin.  Your chart is an eye opener. I'd never seen it done like that before. It is easy to see how the strong 3rd harmonic (E4),  fairly strong 5th harmonic (C#4), and good 6th harmonic (E5)  give the 3rd and 5th interval notes to make a chord.

 

[Johnhamdun]

Good piece of work jmasin.  Your chart is an eye opener. I'd never seen it done like that before. It is easy to see how the strong 3rd harmonic (E4),  fairly strong 5th harmonic (C#4), and good 6th harmonic (E5)  give the 3rd and 5th interval notes to make a chord.

I can post the results of the testing I did a few years back. The results look a great deal like yours but the really interesting thing (and this is what I was talking about before) is
that if you play those same notes through different pieces of wood (we used MDF, Plywood, beautifully grained sitka spruce and everything in between) you get different notes being accentuated. What I found was that when you listened to the differences the ones with more even lines (the pieces of wood that showed the most spikes) sounded richer and the pieces of woods that accentuated notes within the fundamental's major scale sounded sweeter and more "toneful". Going back to what I said earlier, this lead me to believe that there was a scientific reason for why certain woods are considered tone woods.

Its funny that we both looked at a very similar issue and went to the same piece of equipment. A good friend (consequently he also happens to be an engineer) lent me his frequency analyzer when I did my research, haha.

Very cool results ccasion14:, I'll post mine later this week (If I can dig them up)

 

[TimC]

I'm looking forward to seeing your results John. Looking at jmasins' post, I noticed the 7th dissonant harmonic (about 775Hz) that is almost a minor 7th (783.99). Maybe we should start a new thread. We've done a pretty good job of hijacking Volitions Advocate's rebar thread. The node VA grabbed on the rebar must be much like the sweet spot on the face of a golf club head. With a shot hit in the sweet spot, the impact is hardly felt. The further the impact from the sweet spot, the more your hands ring like a bell. I ring a lot of bells.
Edited to ask: jmasin, how was this sample obtained? Off the amp speaker or line out?

 

[jmasin]

Tim, John,

This was off the amp speaker (I used my bassman so it was clean as possible) through a sort of cheap PC mic... all I could lay my hands on at the time.

I'd be up for a new thread.  I was going to start taking some measurements with different p/u combinations and with my other guitars as well to compare.  I was also working on making some of my own pedals, so I'm working on getting setup with a simple Oscope and got my hands on what looks like a decent piece of signal analysis software.

I mean, this is all stuff that effects makers and synthesizer designers already know, but I always find it fun to learn hands on.  That's kind of why I got into engineering in the first place, although it's a far cry from what I actually do from 8-5 every day